What is portable emissions measurement (PEMS) and why is it used?

PEMS (Portable Emissions Measurement System) enables measurement of real-world emissions while driving on public roads, not just laboratory conditions. PEMS equipment installed in the vehicle measures exhaust flow, CO2, CO, NOx, and particle number. It is required for Real Driving Emissions (RDE) compliance in Europe, addressing concerns that laboratory results did not represent actual emissions. RDE tests cover varied routes, altitudes, temperatures, and driving styles. Results must meet conformity factors versus laboratory limits, ensuring emissions control works in real conditions.